This invention relates to the preparation of alkanol alkoxylates by the addition reaction of alkylene oxides with alkanols in the presence of basic catalysts. More specifically, this invention is directed to a process for conducting the alkoxylation reaction of alkanols with alkylene oxides in the presence of basic magnesium-containing catalysts.
Alkanol alkoxylates (or simply alkoxylates, as the terminology is alternatively applied herein) are known materials having utility, for instance, as solvents, surfactants, and chemical intermediates. Alkoxylates in which the alkyl group has a number of carbon atoms in the detergent-range, i.e., from about 8 to 20, are common components of commercial cleaning formulations for use in industry and in the home.
Under conventional practice, alkoxylates are typically prepared by the addition reaction of alkylene oxides with alkanols. In the particular case of the preparation of an ethoxylate (represented by formula III below) the addition of a number (n) of ethylene oxide molecules (formula II) to a single alkanol molecule (formula I) is illustrated by the equation ##STR1## wherein R is alkyl and n is an integer equal to or greater than one. The product of such an alkoxylation reaction is a mixture of various alkoxylate molecules having a variety of alkylene oxide adducts, i.e., a mixture of compounds with different values of n.
Alkoxylation reactions between alkylene oxides and alkanols are known to be necessarily carried out in the presence of a catalyst, which may be either of acidic or basic character. Suitable basic catalysts are known to include the soluble basic salts of the alkali metals of Group I of the Periodic Table, e.g., lithium, sodium, potassium, rubidium, and cesium, and the soluble basic salts of certain of the alkaline earth metals of Group II, e.g., barium, strontium, and calcium. With particular regard to magnesium-containing catalysts as are employed in the process of this invention, the most relevant teachings of the art, specifically, those of U.S. Pat. No. 4,239,917, U.S. Pat. No. 4,210,764, and U.S. Pat. No. 4,233,164 on alkoxylation reactions catalyzed by barium and strontium compounds, indicate only that certain basic magnesium compounds do not effectively promote the alkoxylation of detergent-range alkanols. Other references which describe alkoxylation reactions catalyzed by alkaline earth metal compounds, for instance, the published European patent applications Nos. 26,544, 26,546, and 26,547 and U.S. Pat. Nos. 3,830,850 and 3,637,869 do not mention the use of magnesium compounds as alkoxylation catalysts.
Numerous acidic substances, including broadly the Lewis acid or Friedel-Crafts catalysts and specifically the compound magnesium perchlorate, are also known as effective alkoxylation catalysts. However, the use of acid catalysts is undesirable in several processing aspects. For instance, the acidity of the reaction mixture catalyzes side reactions to produce relatively large amounts of polyalkylene glycols. The acid catalysts also react directly with components of the alkoxylation mixture to yield organic derivatives of the acids which for reasons such as toxicity are not acceptable in the alkoxylate product. Furthermore, efficient use of acid catalysts is generally limited to the alkoxylation of secondary alkanols and to the preparation of alkoxylates having an average number of ethylene oxide adducts that is less than about 2 or 3.